Goats expressing the Swiss Marked pattern have a black (eumelanin pigment) body and belly and tan (phaeomelanin pigment) legs, ears, and facial stripes. The allele

Allele

An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...

 which codes for this pattern is located at the agouti locus of the goat genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

. There are multiple modifier genes

Epistasis

In genetics, epistasis is the phenomenon where the effects of one gene are modified by one or several other genes, which are sometimes called modifier genes. The gene whose phenotype is expressed is called epistatic, while the phenotype altered or suppressed is called hypostatic...

 which control how much tan pigment is actually expressed and so the tan areas can range from pure white to deep red. There may also be present dilution genes

Dilution gene

Dilution gene is a popular term for any one of a number of genes that act to create a lighter coat color in living creatures. There are many examples of such genes:-General:...

which turn the black areas in the pattern to either chocolate or medium brown.